In many complex systems, for the activity f(i) of the constituents or nodes i a power-law relationship was discovered between the standard deviation sigma(i) and the average strength of the activity: sigma(i) proportional variant alpha: universal values alpha=1/2 or 1 were found, however, with exceptions. With the help of an impact variable we present a random walk model where the activity is the product of the number of visitors at a node and their impact. If the impact depends strongly on the node connectivity and the properties of the carrying network are broadly distributed (as in a scale-free network) we find both analytically and numerically nonuniversal alpha values. The exponent always crosses over to the universal value of 1 if the external drive dominates.
